1. Field of the Invention
The present invention relates to an OHP (overhead projector) sheet which is used for printing images, letters or the like by means of a printer in which a ribbon containing hot-melt ink layer composed of coloring material and a binder such wax or the like is utilized, the binder in the ink layer being melted when heated by means of a thermal head or the like while the ink layer is in contact with a recording paper in order to transfer the ink layer to the recording paper.
2. Description of Related Art
Conventionally, a non-porous optical transmission type transparent sheet obtained by coating a transparent plastic film with a binder having a high affinity with the binder of a ribbon and further by performing surface treatment such as antistatic treatment, corona discharge treatment or the like has been utilized as an OHP sheet for a thermal transfer printer.
However, the aforementioned conventional OHP sheet has a low capacity for absorbing hot-melted ink when the OHP sheet is printed by means of a thermal transfer printer because the surface thereof is non-porous. Ordinarily, for full-color printing, ribbons of three colors including yellow, magenta and cyanogen are hit so that the respective colors overlap each other. At this time, ink previously adhered to a sheet is likely to be transferred back to the ribbon together with other ink applied thereafter, thereby lowering the reproducibility and tone representation of the dots in detailed portions.
Because the ink receiving layer is also non-porous and has little cushioning characteristics, when the layer is heated by means of a thermal head, the area in which the thermal head is in contact with the surface of the ink receiving layer decreases remarkably, so that, in a method of representation of density according to tone gradation depending on area size, the color development density of a printed material may be very low.